Current commercial decaffeination of coffee is effected by the removal of caffeine from whole, green coffee beans. The beans are first moistened and then extracted with a solvent which is relatively specific for caffeine. The solvents employed commercially are either a chlorinated hydrocarbon solvent, such as discussed in U.S. Pat. No. 3,671,263 to Patel et al. or a caffeine-deficient water solution of green coffee solubles, such as disclosed in U.S. Pat. No. 2,309,092 to Berry et al.
In the decaffeination process of U.S. Pat. No. 2,309,092 which is commonly referred to as the water extraction system, a caffeine-laden water extract, resulting from contact between caffeine-containing green coffee and the caffeine-deficient water solution, is directly extracted with a solvent in order to remove caffeine. Typically, these solvents are the same chlorinated hydrocarbons which are employed in the direct solvent extraction processes, exemplified by the aforementioned U.S. Pat. No. 3,671,263.
Recently, the coffee industry has developed a number of procedures for decaffeinating green coffee without the use of chlorinated hydrocarbons; however, most of these are more expensive than desired based on current competitive conditions. Among the more promising of these procedures are those which involve contacting the green coffee beans with carbon dioxide in either the liquid or the supercritical state. For example, in U.S. Pat. No. 3,879,569 to Vitzthum et al., there is disclosed a process wherein liquid carbon dioxide is contacted with green coffee beans to extract the caffeine with good selectivity. In another recent patent, U.S. Pat. No. 3,806,619 to Zosel, there is disclosed a decaffeination method wherein near quantitative extraction of caffeine from green coffee beans is achieved through the use of supercritical carbon dioxide. According to this patent, green coffee beans are contacted with carbon dioxide in the supercritical state to extract caffeine. To further improve processing efficiency, with both liquid and supercritical carbon dioxide, the green beans are pre-moistened and the carbon dioxide is saturated with water.
It would be desirable to further improve the decaffeination of both dry and pre-moistened green coffee beans with both liquid and supercritical carbon dioxide.